Abstract : The characteristics of starch were introduced. The research of starch and its application in packaging industry were summarized. The gap between starch properties and foreign countries was pointed out, and the importance of the study of special starch should be emphasized.
Key words: starch; characteristics; research; application; packaging industry
Starch is a renewable natural polymer compound with good adhesion and film-forming properties. The deep processing of corn starch to prepare various kinds of fine chemical products attracts people's attention. People have done a lot of research in the process and application of starch modification to prepare and produce various kinds of adhesives. Starch is a water-soluble compound that is low in price, rich in raw materials, and nontoxic, and is now widely used in packaging and other industries.
1 Starch research and its application in packaging
1.1 Packaging Adhesives
Starch adhesive is a kind of water-soluble adhesive with low price, rich source of raw materials, and no toxicity. It has occupied an extremely important position in the entire packaging paper container material and corrugated cardboard. The corrugated board produced is almost entirely based on starch-based adhesives. Bonded, and because of its excellent performance, oxidized starch adhesives are widely used in the production of single-sided corrugated cardboard. However, due to its unstable viscosity, starch adhesives affect its adhesive properties. In order to improve its adhesive properties, Zhang Qinfa et al. studied the factors affecting the viscosity of oxidized starch adhesives in more detail. The results showed that: when the amount of oxidant (based on the quality of starch) is 18% to 24%, the amount of sodium hydroxide is 1.6% to 2.6%, m (water): m (starch) = 4.5: 5.5, the oxidation time is 15 ~ 25min, the oxidation temperature is 20 ~ 30 °C when the adhesive obtained is relatively good performance, suitable for bonding corrugated paper. The study also found that the use of potassium permanganate as an oxidizing agent prepared in an adhesive storage container was relatively stable.
Starch adhesives have also begun to be used in the manufacture of corrugated board carriers, but due to the use of alkali in the production of traditional corrugated board, it is easy to return moisture. In order to overcome this shortcoming, He Lunying used H, P, Q, W and other substances to study the modification of the carrier starch adhesive. Through the screening test and comprehensive analysis, the optimum formula for the amount of compound additives was determined. The results showed that when the compound additive The amount (in terms of starch mass%) of 11% ~ 12%, the amount of sodium hydroxide is 32%, the adhesive has good flow properties, suitable viscosity, good water retention, can completely and uniformly infiltrate the surface of the adherend, strong bonding ability The addition of multi-functional additives can improve the stability of the adhesive, the difficulty of delamination, gelling and decay, and at the same time, the cost is low. The corrugated paperboard produced by the modified carrier starch adhesive has high bond strength, low moisture repellency, and good cardboard strength. Suitable for corrugated cartons for refrigerated foods.
Plastic products have been widely used in the packaging industry. However, adhesives currently used in plastic packaging containers for adhesive labels have poor adhesive effect, often fall off after the adhesive is dried, lack sufficient affinity for plastics, and have high cost and toxic pollution, such as solvent-based polymerization. Adhesives such as acrylic and polyurethane are sticky, but they are prohibitively used in the food and beverage industry due to their high cost and toxicity. Zeng Defang and others used polyacrylic acid modified starch and added a complex additive to synthesize a green adhesive. The water-soluble acrylic additive B was selected. It was found that adding the auxiliary agent B not only enhanced the bonding strength with the plastic surface, but also improved the adhesive strength of the whole starch adhesive. Auxiliary A is made of several kinds of alcohols. It improves the mutual solubility of auxiliary agent B and starch. It is a good auxiliary solvent and also has a wetting and antifreeze effect. Compared with similar products, the adhesive has the advantages of non-toxic, non-polluting, and good adhesiveness, and is widely used for the trademark adhesive in the plastic packaging industry.
1.2 modified starch packaging film
The commonly used food packaging materials at home and abroad are mainly polyethylene, cellophane, and man-made fibers. They cannot be degraded in nature, and these packaging discards cause environmental pollution. On the other hand, the mechanical strength of edible films is insufficient. In order to overcome these shortcomings, many domestic and foreign scholars have conducted research in this regard. Li Zhida et al. used a physicochemical method to separate amylose content of about 80% starch material and isoamylase-modified starch (chain starch content about 40%), and added additives at the same time to study its film forming properties. Experiments show that the proper combination of sorbitol and glycerol is a good edible plasticizer, CMC-Na is a good strength enhancer, and animal protein hydrolysates can solve the problem of uncovering membranes. Through the reaction, a water-insoluble starch-edible edible starch film with good tensile properties, transparency, and folding-resistance is obtained, and has broad development prospects in food packaging.
Starch is a strongly polar hydrophilic material, while LDPE is a hydrophobic material with very small polarity. The structure and polarity of the two are very different. In order to increase the starch filling amount, the starch is evenly distributed in the LDPE, and the starch needs to be modified. Zhang Huaji used oxidized polyethylene (OPE) as a compatibilizer for the starch-filled LDPE blend system, and developed homemade photodegradation accelerators for LDPE blends filled with lanthanum octanoate, lauric acid yttrium, and barium stearate. Degradable LDPE masterbatch and film. The composition of starch/stearic acid persimmon blend system was studied. The hydrophobic treatment of starch with aluminate was discussed. The compatibilization of oxidized polyethylene to starch/LDPE blend system was discussed. The LDPE index of photocatalytic degradation of osmium stearate was studied. Impact, performance tests and application tests were performed on LDPE packaging films containing 20% ​​starch and 0.4% barium stearate. The results show that the mechanical properties and hygienic properties meet the requirements of national standards. After being buried for one year, the fragments are degraded into fragments smaller than 25 cm and gradually assimilated by the soil, which reduces the pollution to the environment.
1.3 All-starch plastic packaging
With the increasing awareness of environmental protection, various countries are developing environmentally friendly packaging materials. Currently, starch degradation resins and whole-starch thermoplastics have achieved certain results.
The so-called starch degradation resin is to blend the biomaterial starch and degradation promoter with synthetic resin. Under the action of microorganisms, high temperature and oxygen, the polymer chain in the plastic breaks, the molecular weight decreases, and finally it is converted into CO2, water and biological organic matter. The development and use of this type of resin can partially solve the pollution caused by plastics. All-starch plastic is a kind of plastic made from starch and a small amount of degradable plasticizer. It can be completely biodegraded without pollution after use. The research progress of full-starch plastics is fast, especially suitable for food, medicine, health and other aspects. The packaging, at present all countries are strengthening research in this area. Judging from the current research situation, all-starch plastics are better for extrusion blow molding, but they can only produce films with a thickness of 20 μm or more. The stability of injection-molded rigid products is good. However, there are still defects such as low pressure resistance, poor toughness, and fragility in applications such as blowing, calendering, and vacuum blister.
In addition, starch-based fully biodegradable plastics have developed rapidly and many industrialization results have been achieved. In order to improve the compatibility of starch and polymer blends, the starch must be processed. The surface of the modified starch granules is covered with alkyl groups, which weakens the effect of hydrogen bonding and improves the compatibility with some resins. The blending performance is stronger than the original starch filling system. Plastics made abroad using this method have been applied to packaging materials, containers and films. China also conducts research in this area, but there is still a gap with foreign countries.
1.4 Modified Starch and Protein Packaging Materials
Modified starch and protein packaging materials are mainly used for food packaging and making disposable tableware.
1.4.1 Modified Starch Packaging Materials
Starch is a natural polymer material, which is inexpensive, renewable, and naturally degraded in the natural environment after being discarded. It can also be eaten or used as a feed. The starch is cross-linked with a compound containing a hydrophobic group and the resulting cross-linked product is water-resistant. This material is mainly used to make disposable tableware. The main raw materials are tapioca starch, wheat starch, corn starch.
1.4.2 Original starch and protein film packaging materials
The original starch and protein film packaging materials are often used to make inner packaging bags and package water-containing foods to prevent the spread of flavors inside the bags. Protein films and other papers, starches made of composite materials for food packaging. Dishware made of raw starch and paper needs to be coated with a waterproof film on its surface due to its poor waterproof performance. Waterproof membranes are usually made of protein, the most common being corn protein. Zein contains 40% gliadin. It is composed of molecules, 25,000 to 40,000 proteins. Since the amino acid terminal of prolamin has a nonpolar hydrophobic group such as leucine and alanine, its hydrophobicity is increased, and an edible packaging film can be prepared by using glycerol and propylene glycol as plasticizers. The film is very oil-proof, waterproof, and high-temperature resistant and can therefore be used for the production of disposable tableware.
1.5 Supermicro Starch Packaging Materials
Using modern super powder technology, the raw material is crushed into particles of 3~1μm called superfine powder. Starch-based biodegradable plastics made using this technology have significant advantages. The ultra-fine starch is small and uniform in size, and has a large specific surface area, so that the fluidity and filling properties are remarkably improved. The biodegradable plastics prepared therefrom can effectively improve the mechanical properties of the materials and can ensure the performance of the materials. Under the premise, the amount of starch is greatly increased, which is of great significance for reducing the cost, developing the application of natural starch, and increasing the biodegradation rate of the plastic.
Wu Jun et al. prepared ultra-fine starch by a combination of high-speed jet mill and ball mill. It was found that when the average particle size of ultrafine starch was 3.126 μm, the crystallinity decreased from 38.7% to 17.1%. After glycerol plasticization, the ultra-low starch crystallinity is as low as 9.3%, its processing performance has been greatly improved, and food-grade biological product packaging films can be prepared. The mechanical properties and biodegradability of the ultra-fine starch-based film are good. , On the premise of ensuring good material properties, the degraded starch has good oil resistance and air permeability, can be used for general food packaging, and can also be used for fresh air conditioning and preservation of fruits and vegetables to prevent the production of large amounts of CO2 due to respiration during packaging of fresh fruits and vegetables. Damage caused.
2 Conclusion
The use of starch in the packaging industry has greatly reduced the application of non-degradable materials in the packaging industry, to a certain extent ease the pressure on the ecological environment, save resources, reduce environmental pollution, and has great significance in the packaging industry. However, there are still problems in the packaging industry in China, such as the product is not stable, and the scope of application is not extensive. There is still a gap between the technology of starch in special packaging and foreign countries. Therefore, it is particularly important to strengthen the study of starch, especially the multifunctional starch packaging materials. Starch has a broad development prospect in the packaging industry. (Wen / Zhu Lihong Fu Heqing)
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